CALIFORNIA 
AGRICULTURAL  EXTENSION  SERVICE 

CIRCULAR  19 

MAY,  1928 


ARTIFICIAL  INCUBATION 
OF  EGGS 


J.  E.  DOUGHERTY 


PUBLISHED    BY 

THE  COLLEGE   OF  AGRICULTURE 
UNIVERSITY  OF  CALIFORNIA 


Cooperative  Extension  work  in  Agriculture  and  Home  Economics,  College  of  Agriculture, 
University  of  California,  and  the  United  States  Department  of  Agriculture  cooperating.  Dis- 
tributed in  furtherance  of  the  Acts  of  Congress  of  May  8  and  June  30,  1914.  B.  H.  Crocheron, 
Director,  California  Agricultural  Extension  Service. 


UNIVERSITY  OF  CALIFORNIA   PRINTING  OFFICE 

BERKELEY,   CALIFORNIA 

1928 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/artificialincuba19doug 


ARTIFICIAL  INCUBATION  OF  EGGS1 

J.  E.  D0UGHEETY2 


At  the  beginning  of  the  year  1926,  there  were  262  commercial 
hatcheries  located  in  thirty-seven  different  counties  of  California, 
each  of  which  had  an  incubating  capacity  of  more  than  1,000  eggs. 
The  total  capacity  of  the  larger  hatcheries  in  the  state  was  7,781,342 
eggs  at  that  time  and  the  grand  total,  including  both  small  and  large 
hatcheries,  was  estimated  to  be  approximately  8,000,000  eggs,3  It  has 
been  materially  increased  since  that  estimate  was  made. 

In  addition  to  the  chicks  produced  in  commercial  hatcheries,  a 
considerable  percentage  of  farmers  and  poultry  keepers  hatch  eggs 
from  their  own  flocks,  During  the  past  year  many  farmers  have  also 
begun  to  use  incubators  for  the  hatching  of  their  turkey  eggs,  It 
has  been  demonstrated  at  the  University  Farm  that  turkeys  can  be 
hatched  and  reared  equally  as  well  artificially  as  by  natural  methods, 
and  the  time  and  rate  of  hatching  controlled  to  better  advantage. 

It  is  evident  that  artificial  incubation  is  growing  in  popularity. 
As  the  use  of  incubators  becomes  more  widespread,  there  is  a  larger 
demand  for  comprehensive  information  concerning  how  to  operate 
them  to  obtain  most  effective  results. 

SELECTING    EGGS    FOR    HATCHING 

The  eggs  that  are  to  produce  the  future  layers  should  be  carefully 
selected  for  (1)  size,  (2)  shape,  (3)  color,  (4)  quality  of  shell.  Size, 
shape  and  color  of  the  egg  are  largely  inherited,  as  pointed  out  by 
Benjamin  (1920). 4  Such  inheritance  is  also  evidenced  by  the  fact  that 
the  production  of  large  eggs  is  a  breed  characteristic  of  the  Minorca, 
white  eggs  a  breed  characteristic  of  the  Leghorn,  and  brown  eggs  a 
breed  characteristic  of  the  Plymouth  Rock.  Weak-shelled  eggs  break 
more  easily  when  being  turned  in  the  incubators  than  eggs  of  good 
shell  quality  and  may  ' '  dry  down ' '  too  rapidly,  due  to  the  shell  being 
more  porous. 


i  This  circular  applies  only  to  natural  draft  incubators.  The  forced  draft 
and  agitated  air  types  of  mammoth  incubators  are  of  such  recent  development 
that  sufficiently  extended  data  on  their  operation  to  warrant  publication  is  not 
yet  available. 

2  Associate  Professor  of  Poultry  Husbandry  and  Associate  Poultry  Husband- 
man in  the  Experiment  Station. 

3  Data  from:  Voorhies,  Edwin  C.  The  California  poultry  industry:  a  statis- 
tical study.     California  Agr.  Exp.  Sta,  Bui.  413:1-172.     1926. 

■i  The  references  cited  may  be  found  at  the  end  of  this  circular. 


4  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  19 

Continued  selection  of  hatching  eggs  for  the  most  desirable  size, 
shape,  and  color  should  result  in  the  development  of  a  strain  produc- 
ing an  increased  percentage  of  such  eggs  from  year  to  year  since 
like  tends  to  produce  like  with  reference  to  these  characters.  In  the 
case  of  tinted  eggs  laid  by  white  egg  breeds,  however,  Benjamin 
(1920)  and  Dougherty  and  Gossman  (1923)  observed  that  the  brown 
tint  may  gradually  fade  out  as  production  increases  in  early  spring. 
The  elimination  of  tinted  eggs  from  those  used  for  hatching  after  the 
time  when  the  less  strongly  tinted  eggs  have  faded  sufficiently  so  that 
they  cannot  be  readily  distinguished  from  eggs  laid  by  hens  that 
always  lay  white  eggs  is,  therefore,  of  little  value ;  it  will  not  decrease 
the  " taint"  of  tint  in  the  breeding  flock  and  perfect  a  strain  that  is 
genetically  pure  for  whiteness  of  egg  shell.  This  can  only  be  done 
in  stock  producing  tinted  eggs  by  trapnesting  the  breeding  hens  to 
identify  and  remove  the  layers  of  tinted  eggs  from  the  flock,  and  by 
using  males  known  to  be  genetically  pure  with  respect  to  this  factor. 
Trapnesting  to  identify  hens  laying  tinted  eggs  should  be  done  after 
the  molting  season  and  before  spring  production  has  increased  suffici- 
ently to  cause  enough  fading  of  any  of  the  tinted  eggs  laid  to  make 
them  difficult  to  distinguish  from  white  eggs. 

EFFECT  OF   TEMPERATURE   ON    EGGS    HELD    FOR    HATCHING 

That  eggs  being  held  for  hatching  can  be  subjected  to  temperatures 
closely  approaching  the  freezing  point  has  been  shown  by  a  number 
of  investigators.  Elford  (1921)  exposed  a  number  of  lots  of  eggs 
packed  in  different  ways  to  temperatures  ranging  from  14°  to  26° 
Fahrenheit,  for  15  minutes  to  5  hours,  and  obtained  results  indicating 
that  strong-germed  eggs  will  stand  more  cold  than  it  has  been  con- 
sidered safe  to  expose  them  to.  Mauro  (1923)  found  that  eggs  kept 
in  a  refrigerator  at  32.9°  F  for  24  hours  were  not  appreciably  affected. 
But  when  held  at  this  temperature  for  48  hours  the  capacity  of  the 
embryos  to  develop  was  considerably  reduced,  and  after  72  hours  of 
such  refrigeration,  it  was  entirely  destroyed.  Mussehl  and  Bancroft 
(1924)  found  that  exposure  of  hatching  eggs  to  a  temperature  of 
32°  F  for  6  to  18  hours  did  not  lower  their  hatching  power  or  result 
in  an  unusual  number  of  crippled  or  otherwise  abnormal  chicks. 
Dougherty  (1926)  found  that  exposure  of  eggs  held  for  hatching  to 
temperatures  of  28°  to  32°  F  for  four  successive  nightly  periods 
(putting  them  in  the  ice  box  at  5  p.m.  and  removing  them  to  a  room 
temperature  of  60°  F  at  7  a.m.),  plus  a  continuous  period  of  38  hours 
did  not  result  in  any  significant  reduction  in  the  per  cent  of  chicks 


1928 


ARTIFICIAL    INCUBATION    OF    EGGS 


hatched.  He  states  that  a  sufficiently  long  exposure  to  a  temperature 
of  32°  F  would  probably  have  a  detrimental  effect  on  hatchability 
but  the  brief  periods  of  low  temperature  to  which  eggs  may  be  exposed 
in  the  poultry  districts  of  California  are  evidently  not  cold  enough 
or  of  sufficient  duration  to  cause  any  serious  injury  to  hatching  eggs. 
The  maximum  temperature  at  which  to  hold  eggs  being  saved  for 
hatching  is  generally  conceded  to  be  below  70°  F.  Edwards  (1902) 
found  that  the  lowest  temperature  at  which  development  can  occur 
lies  between  68°  and  69.8°  F.  Gowell  (1902)  held  one  lot  of  eggs  at 
70°  and  another  lot  at  50°  F  for  10  days  and  those  held  at  70°  hatched 
slightly  better  than  the  other  lot.  In  this  case,  however,  the  hatches 
were  poor  and  the  data  meager,  so  that  the  results  cannot  be  given 
much  weight.  Philips  (1909)  held  three  lots  of  eggs  for  14  days  at 
50°,  65°,  and  80°  F  respectively  before  hatching.  The  corresponding 
hatching  results  obtained  were  70.4,  43.1,  and  0  per  cent.  Just  why 
the  lot  held  at  65°  hatched  so  poorly  is  not  clear.  Under  the  con- 
ditions existing  in  California  there  is  apparently  more  danger  of 
getting  hatching  eggs  too  warm  than  of  getting  them  too  cold.  A 
temperature  range  of  40°  to  60°  F  would  appear  to  be  well  within 
the  limits  of  safety. 


EFFECT  OF  AGE  AND  METHOD  OF  HANDLING  ON  EGGS  FOR 

HATCHING 

In  table  1  is  given  the  results  of  the  first  of  a  series  of  trials  being 
made  at  this  Station  to  determine  the  effect  of  age  and  of  method  of 
holding  on  eggs  being  saved  for  hatching.     These  eggs  were  held  on 


TABLE  1 
Effect  of  Age  and  of  Daily  Turning  on  Eggs  Being  Held  for  Incubation 


Treatment 

Age  of  eggs 
days 

Per  cent 

fertile  eggs 

hatched 

Eggs  held  on  sides  in  open  rack  and  not  turned < 

6 
10 
14 

6 
10 
14 

6 

10 
14 

6 

10 
14 

70.0 
69.6 
60.0 
76.2 
82  6 

Eggs  held  on  sides  in  covered  egg  case  and  not  turned - 

74.4 
57.8 
66.0 
54.8 

79.6 
73  4 

1 

72.0 

6  CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE  [ClRG.  19 

their  sides  in  a  cool  cellar  and  set  April  1.  The  data  obtained  do 
not  indicate  that  the  age  of  the  eggs  up  to  10  days  or  the  use  of  open 
racks  as  compared  with  covered  egg  cases  have  any  significantly 
detrimental  effect  on  hatching  quality.  But  whether  eggs  are  turned 
or  not  while  being  held  for  hatching  is  evidently  important,  for 
the  average  hatch  of  chicks  to  fertile  eggs  set  was  63  per  cent  in  the 
case  of  the  two  groups  of  eggs  that  were  not  turned  and  76.4  per  cent 
for  the  two  groups  that  were  turned. 

An  egg  case  is  a  convenient  receptacle  in  which  to  save  and  turn 
hatching  eggs.  If  the  eggs  are  held  on  end  with  the  small  ends  down, 
they  can  be  readily  turned  by  elevating  one  end  of  the  case  eight  or 
more  inches  one  day  and  the  opposite  end  the  next.  If  held  on  their 
sides,  the  full  number  of  fillers  would  have  to  be  in  the  case  and  the 
cover  fastened  on  before  turning.  In  turning  the  case  would  be  laid 
on  one  side  the  first  day,  on  one  end  the  second  day,  on  the  other  side 
the  third  day,  etc.  Revolving  the  case  in  this  way  from  day  to  day 
would  give  the  eggs  a  full  quarter  turn  and  hold  them  in  their  natural 
position.  What  brief  data  there  is  available,  however,  as  well  as  the 
opinion  of  a  large  number  of  experienced  hatcherymen,  indicate  that 
whether  eggs  are  held  on  their  sides  or  stood  on  the  small  ends  is  of 
little  consequence  for  the  first  week,  if  turned  daily.  But  if  held 
much  longer  than  one  week  it  is,  perhaps,  better  to  keep  them  on  their 
sides  throughout  the  holding  period. 

Holding  the  eggs  too  long  may  also  reduce  hatching  quality.  The 
average  hatch  of  chicks  to  fertile  eggs  (table  1)  was  70.9  per  cent  for 
the  four  lots  of  eggs  held  6  days;  72.9  per  cent  for  those  held  10  days; 
and  65.3  per  cent  for  those  held  14  days.  Waite  (1919)  found  that 
there  wras  a  progressive  decrease  in  hatchability  as  the  age  of  hatching 
eggs  increased  beyond  one  week.  Dareste  (1883)  reported  that  the 
longer  eggs  were  held  before  setting  the  greater  was  the  per  cent  of 
abnormal  embryos.  The  sooner  eggs  were  set  after  being  laid  the 
better. 

THE    INCUBATOR    ROOM 

A  well  ventilated  room  where  the  temperature  remains  at  approxi- 
mately 60°  F  is  the  most  desirable  environment  for  an  incubator.  A 
basement  or  semi-basement  will  usually  come  nearer  to  providing 
desirable  temperature  conditions  than  a  room  above  ground  because 
of  being  better  protected  from  outside  weather  conditions,  If  built 
above  ground,  well  insulated  walls  and  a  double  roof  may  be  required. 


!928]  ARTIFICIAL   INCUBATION    OF   EGGS  7 

A  concrete  floor  is  preferable  to  a  dirt  or  board  floor  only  because 
it  is  easily  kept  clean  and  sanitary  and  is  very  durable.  There  is  also 
less  objection  to  wetting  down  a  concrete  floor  when  it  is  desired  to 
increase  the  humidity  of  the  incubator  room  in  this  way  when  eggs 
are  hatching. 

Good  ventilation  as  well  as  satisfactory  lighting  of  an  incubator 
room  can  be  obtained  by  the  proper  installation  of  windows  and 
exhaust  ventilators,  Transom  or  cellar  sash  should  be  placed  near  the 
ceiling  (a  ceiling  not  less  than  8  feet  high  for  single  deck  machines 
and  9  feet  for  multi-deck  machines  is  recommended)  on  one  or  more 
sides  of  the  room  for  the  intake  of  fresh  air.  One  or  more  exhaust 
ventilators  at  least  8  inches  in  diameter  should  be  located  on  the  wall 
opposite  the  windows,  or  down  the  center  of  the  room  if  windows  are 
on  both  sides.  The  windows  should  be  well  above  ground  level  and 
spaced  approximately  6  feet  apart.  They  should  be  hinged  at  the 
bottom  to  swing  in,  and  have  triangular  side  shields  attached  to  the 
window  frames.  These  side  shields  force  all  incoming  fresh  air  over 
the  top  of  each  window  when  open,  and  help  to  prevent  drafts,  A 
light-weight,  removable,  burlap  covered  frame  made  to  rest  on  top 
of  the  wooden  side  shields  and  to  fully  cover  each  window  opening 
when  the  windows  are  open  can  be  provided,  if  necessary,  for  use  on 
windy  days,  It  will  reduce  the  velocity  of  the  incoming  fresh  air  and 
prevent  the  setting  up  of  strong  enough  air  currents  in  the  incubator 
room  to  affect  the  incubator  lamps,  if  lamps  are  used,  or  the  tempera- 
tures of  any  of  the  machines. 

One  exhaust  ventilator  should  be  sufficient  for  approximately  300 
square  feet  of  floor  space.  It  should  be  built  with  the  bottom  about 
18  inches  above  the  floor  and  the  top  extending  well  above  the  highest 
point  of  the  roof ;  the  higher  the  top  of  this  ventilator  and  the  more 
efficient  the  ventilator  cap,  the  stronger  will  be  the  suction  (revolving 
metal  caps  have  been  found  more  effective  than  stationary  caps). 
This  ventilator  should  be  provided  with  a  conveniently  located  damper 
to  regulate  the  amount  of  air  passing  through  it  so  as  not  to  exhaust 
the  air  from  the  room  too  rapidly.  A  trap  door  in  the  ventilator  near 
the  ceiling,  as  well  as  one  or  more  large  ceiling  ventilators,  may  also 
prove  of  value  in  removing  hot  air  from  the  incubator  room  in  very 
warm  weather  and  preventing  the  temperature  from  rising  unduly. 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  19 


GETTING   THE   INCUBATOR   READY 

Before  the  opening  of  the  hatching  season  each  year,  the  incubators 
should  be  inspected  to  see  that  they  are  in  good  working  order.  If 
any  of  the  incubators  have  the  ether  wafer  type  of  thermostat,  an 
extra  wafer  should  be  kept  on  hand  in  case  one  of  those  in  use  should 
become  corroded  and  allow  the  vaporized  ether  to  escape. 

The  incubator  should  be  leveled  with  a  spirit  level.  If  the  egg 
trays  in  natural  draft  machines  are  not  all  on  the  same  level,  the  eggs 
that  are  high  will  be  subjected  to  a  higher  temperature  than  those 
that  are  lower. 

The  even  distribution  of  heat  to  all  parts  of  the  egg  chamber  can 
be  checked  by  first  operating  the  incubator  without  eggs  but  with  a 
number  of  thermometers  located  at  different  places  on  the  egg  trays 
and  having  the  thermometer  bulbs  l1/^  inches  above  the  bottoms  of 
the  trays.  If  the  temperature  readings  show  a  distinctly  uneven  dis- 
tribution of  heat,  the  cause  should  be  looked  for,  and  corrected  if 
possible,  before  the  incubator  is  set. 

If  temperature  variations  in  different  parts  of  the  egg  chamber  do 
not  exceed  1%  degrees  any  harm  to  the  eggs  that  might  accrue  from 
this  amount  of  unevenness  may  be  largely  neutralized  by  the  method 
of  manipulating  the  eggs.  For  example,  the  position  of  the  trays  can 
be  changed  one  or  more  times  daily ;  the  trays  can  be  turned  end  for 
end ;  the  position  of  the  eggs  on  the  trays  can  be  changed ;  or  a 
combination  of  such  manipulations  can  be  used,  depending  on  the 
style  of  incubator. 

Testing  Electric  Incubators. — Electric  incubators  should  be  heated 
to  operating  temperature  to  be  certain  that  there  are  no  breaks  or 
short  circuits  in  the  wiring  and  that  the  thermostatic  regulator  is 
working  smoothly.  The  breaker  contact  points  should  be  lightly  filed 
with  a  fine  magneto  file  to  clean  them  and  make  the  contact  surfaces 
perfectly  flat  and  parallel  to  each  other.  A  full  contact  of  the  points 
is  necessary  to  reduce  arcing  to  a  minimum. 

Oil  and  Gas  Heated  Incubators. — The  lamp  of  each  lamp  heated 
machine  should  be  thoroughly  cleaned  before  using,  each  season,  the 
burner  boiled  in  a  solution  of  washing  soda,  and  a  new  wick  put  in, 
if  necessary.  If  gas  burners  are  used  they  should  be  examined  to 
see  that  they  are  in  good  working  order. 

In  beginning  the  hatch  a  medium  flame  is  best,  for  if  too  small  a 
flame  be  used  to  start  with  it  cannot  be  turned  low  enough  at  the 


L928 


ARTIFICIAL    INCUBATION    OF    EGGS 


end  of  the  hatch  in  warm  weather  to  keep  the  temperature   from 
running  up.     If  too  high  a  flame  is  used  the  lamp  will  smoke. 

Lamps  should  be  trimmed  and  filled  each  day  after  turning  the 
eggs.  If  filled  before  turning,  the  hands  may  become  oily  enough  to 
leave  oil  on  the  eggs  when  turning  them  and  perhaps  injure  the 
embryos.  The  wick  can  be  most  easily  trimmed  by  covering  the  end 
of  the  finger  with  a  piece  of  cloth  and  rubbing  off  the  charred  crust. 
After  turning  the  wick  just  high  enough  to  expose  the  charred  part 
above  the  wick  tube,  the  top  of  the  wick  should  be  wiped  off  in  one 
direction  only ;  this  lays  all  the  threads  of  the  wick  in  the  same  direc- 
tion and  results  in  a  better  shaped  flame.  After  wiping,  the  wick  is 
turned  up  a  bit  and  the  corners  patted  down  to  do  away  with  a  high 
cornered  flame  that  would  smoke.  The  flame  should  be  straight  across 
the  top  and  have  rounded  corners. 

Disinfection, — Before  every  hatch  the  incubator  and  trays  should 
be  thoroughly  cleansed  and  disinfected.  If  convenient  the  movable 
parts  should  be  placed  in  the  sun  to  dry  and  air  as  direct  sunshine  is' 
a  most  effective  germicide.  Disinfection  of  the  incubator  is  most 
easily  done,  perhaps,  with  a  suitable  spray  pump  using  about  a  2  per 
cent  solution  of  some  good  preparation  such  as  formalin,  a  sodium 
hypochlorite  disinfectant,  a  cresol  compound,  or  any  of  the  phenol 
disinfectants.  In  the  case  of  the  phenol  disinfectants  (commonly 
known  as  coal  tar  sprays  or  sheep  dips)  care  should  be  taken  to  use, 
for  the  incubators,  only  carefully  manufactured  preparations  that 
are  thoroughly  emulsified  and  do  not  leave  an  oily  or  sticky  residue. 

Germicides  may  vary  greatly  in  strength  as  shown  by  their  carbolic 
or  phenol  coefficients.  The  phenol  coefficient  of  a  disinfectant  is  an 
indication  of  its  germicidal  value  as  compared  with  pure  carbolic  acid. 
In  order  that  the  purchaser  may  more  fully  determine  the  worth  of 
proprietary  phenol  disinfectants,  the  phenol  coefficient  should  appear 
on  the  label.  For  example,  a  disinfectant  having  a  phenol  coefficient 
of  5  has  been  found  by  test  to  act  five  times  more  rapidly  in  destroying 
typhoid  bacteria  in  pure  culture  than  pure  carbolic  acid  or  phenol. 

Thermometer. — The  incubator  thermometer  should  be  tested  for 
accuracy  every  season  by  comparing  it  with  a  clinical  or  fever  ther- 
mometer. This  is  best  done  by  placing  both  thermometers  in  hike 
warmwater  at  approximately  103°  F.  With  bulbs  close  together  and 
while  stirring  the  water,  the  thermometer  readings  should  be  taken. 
The  difference  in  reading,  if  any,  between  clinical  and  incubator 
thermometer  will  represent  the  amount  in  degrees  that  the  incubator 


10  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  19 

thermometer  is  inaccurate.    It  is  the  better  plan  to  destroy  inaccurate 
thermometers  and  use  only  accurate  ones. 

Setting  the  Eggs. — The  incubator  should  be  accurately  regulated 
to  provide  proper  temperature,  ventilation,  and  moisture  conditions 
before  the  eggs  are  set.  It  is  just  as  important  that  embryonic 
development  be  started  under  the  most  favorable  environmental 
conditions  as  it  is  that  it  be  continued  and  concluded  under  such 
conditions.  Failure  to  utilize  the  utmost  care  from  the  very  beginning 
in  regulating  the  incubator,  and  in  handling  the  eggs  to  prevent 
unnecessary  jarring,  may  contribute  materially  to  the  "in-shell" 
mortality  during  the  hatching  period. 


OPERATING   THE    INCUBATOR 

Temperature. — Experimental  work  (1915)  at  this  station  has 
shown  that  the  temperature  throughout  the  hatch  in  incubators  with 
natural  air  circulation  should  be  102  degrees  when  the  center  of  the 
thermometer  bulb  is  on  a  level  with  the  tops  of  the  eggs.  Whether 
it  touches  a  fertile  egg  or  not  is  unimportant.  If  the  thermometer  is 
hung  so  that  the  center  of  the  bulb  is  above  or  below  the  tops  of  the 
eggs,  the  temperature  must  be  run  higher  or  lower  than  102  degrees 
as  indicated  in  figure  1.  Similar  results  were  obtained  by  Philips 
(1923).  The  heat  in  this  type  of  incubator  usually  comes  into  the 
egg  chamber  from  the  top  so  that  the  nearer  the  thermometer  is  to 
the  top  of  the  egg  chamber  the  higher  it  will  read.  It  is,  perhaps, 
most  convenient,  however,  to  maintain  the  same  thermometer  reading 
from  day  to  day  throughout  the  incubation  period  and  not  have  to 
remember  to  lower  or  raise  this  reading  from  time  to  time.  This  can 
be  done  if  the  position  of  the  thermometer  is  such  that  the  center  of 
the  bulb  is  level  with  the  tops  of  the  eggs. 

Ventilation. — Good  ventilation  is  a  very  important  factor  in  the 
process  of  incubation.  During  growth,  the  embryo  is  nourished  by 
the  supply  of  stored-up  food  in  the  egg.  In  order  to  utilize  this  food 
and  transform  it  into  new  body  tissue,  into  heat,  or  into  muscular 
action  such  as  the  pumping  of  the  blood  through  the  blood  vessels, 
oxygen  is  necessary.  The  network  of  blood  vessels  which  extends 
close  to  the  inside  of  the  shell  and  to  the  air  cell,  takes  up  oxygen 
from  the  fresh  air  that  enters  through  the  pores  of  the  shell  and 
throws  off  carbon  dioxide,  which  passes  out  through  the  shell.  Briefly 
stated,  the  developing  embryo  breathes  in  fresh  air  and  gives  off 
carbon  dioxide  through  the  pores  of  the  shell. 


1928 


ARTIFICIAL    INCUBATION    OF    EGGS 


11 


The  air  cell  plays  an  important  part  in  this  respiratory  process  as 
evidenced  by  the  fact  that  stopping  up  the  pores  of  the  shell  over 
the  air  cell  will  more  seriously  injure  the  embryo  than  will  stopping 
the  pores  of  any  other  part  of  the  shell.  As  the  embryo  grows  the 
air  cell  enlarges  due  to  loss  of  water  and  shrinking  of  the  shell 
content ;  and  in  so  doing,  an  increasingly  larger  air  space  is  provided 
from  day  to  day  into  which  carbon  dioxide  and  water  vapor  can  be 
discharged  and  from  which  oxygen  can  be  taken  up.  This  continued 
increase  in  size  of  the  air  cell  of  a  normally  developing  egg  from 


/06 
k 

% 

IT) 

too 


Ho.l  Thermometer  with    center  of  bu/b 
■i",  a  bo  re   tops   of*  egos. 


/Vo.£   Thermometer  w/th  center  ^ 
of  bu/b  /eye/  w//b  tops  of  eggs,  y 


Ho.3  TKZZO^^ 

bulb  level  *"*>  cenTero  f 


FIRST   WEEK 


3ECOHD   WEEK 


Tti/RO   WEEK 


Fig.  1. — The  trend  of  temperature  readings  from  week  to  week  during 
incubation.  Thermometer  No.  1,  suspended  with  center  of  bulb  %  inch  above 
the  eggs,  registers  higher  at  first  than  thermometer  No.  2,  which  is  on  a  level 
with  the  tops  of  the  eggs,  because  it  is  closer  to  the  source  of  the  heat  in  the 
top  of  the  egg  chamber.  Thermometer  No.  3,  with  center  of  bulb  level  with 
center  of  eggs,  registers  lower  than  No.  2  as  it  is  further  away  from  the  top 
of  the  egg  chamber.  As  the  embryos  grow,  however,  and  the  heat  given  off  by 
the  eggs  increases,  less  artificial  heat  is  required.  Since  thermometer  No.  1  is 
y>2  inch  above  the  eggs  and  affected  more  by  the  artificial  heat  from  the  top 
of  the  egg  chamber  than  by  the  natural  heat  from  the  eggs,  it  will  read  lower 
from  day  to  day  as  the  artificial  heat  is  reduced,  whereas  thermometer  No.  3, 
which  is  further  from  the  top  of  the  egg  chamber  and  down  between  the  eggs, 
will  read  higher  and  higher,  due  to  the  increasing  heat  from  the  eggs  as  the 
embryos  grow. 


the  first  to  the  twentieth  day  of  incubation,  paralleling,  as  it  does,  the 
growth  of  the  embryo  and  its  ventilation  requirements,  may  be  looked 
upon  as  indicative  of  the  continual  increase  in  its  oxygen  require- 
ments. As  explained  further  under  the  section  on  moisture,  it  serves 
as  a  guide  to  the  incubator  operator  in  indicating  whether  or  not  the 
rate  of  flow  of  fresh  air  through  the  egg  chamber  and  the  humidity 
of  this  air  are  meeting  the  needs  of  the  developing  eggs.  Hannas 
(1920)  measured  the  air  cells  of  several  thousand  eggs  in  an  effort 
to  determine  the  proper  size  of  air  cell  at  different  stages  of  incuba- 
tion. He  reports  the  depth  of  the  air  cell  to  be  2%2  of  an  inch  on  the 


12  CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE  [ClRC.  19 

8th  day,  between  2*%2  and  ]%6  of  an  inch  on  the  14th  day,  and 
between  15/1Q  and  3%2  of  an  inch  on  the  19th  day.  He  states  that 
these  measurements  were  found  to  be  approximately  equivalent  to  an 
air  cell  a  little  less  than  one-third  the  size  of  the  egg  on  the  8th  day, 
one-third  the  size  of  the  egg  on  the  14th  day,  and  two-fifths  the  size 
of  the  egg  on  the  19th  day. 

The  ventilation  of  the  incubator  should  be  such  as  to  carry  fresh 
air  into  the  egg  chamber  as  rapidly  as  needed  and  to  carry  carbon 
dioxide  away  as  rapidly  as  it  is  given  off  by  the  eggs.  Insufficient 
ventilation  will  seriously  injure  the  developing  embryos  by  depriving 
them  of  enough  oxygen  and  causing  the  carbon  dioxide  content  of 
the  air  surrounding  the  eggs  to  increase.  Lamson  and  Edmond  (1914) 
found  that  if  the  carbon  dioxide  content  of  the  air  about  the  eggs 
increased  beyond  150  parts  in  10,000  there  was  a  high  mortality  of 
the  embryos,  which  rose  still  higher  when  it  exceeded  200  parts  in 
10,000.  Too  much  ventilation,  at  least  after  the  first  week,  probably 
cannot  be  given,  provided  proper  temperature  and  moisture  con- 
ditions are  maintained  in  the  egg  chamber. 

Hatching  eggs  require  very  little  ventilation  the  first  day  or  two 
of  incubation.  Therefore,  in  incubators  equipped  with  adjustable 
ventilators,  these  can  be  almost  closed  the  first  two  days  and  then 
opened  more  and  more  as  the  incubation  period  advances,  using  the 
gradual  increase  in  the  size  of  the  air  cell  or  the  loss  in  weight  of  the 
eggs,  or  both,  to  guide  one  in  determining  their  proper  adjustment. 
This  is  discussed  in  detail  in  the  section  on  moisture. 

A  properly  designed  incubator  should  permit  of  sufficient  control 
of  ventilation  to  meet  changing  weather  conditions  as  well  as  the 
changing  requirements  of  the  developing  embryo  within  the  egg. 
Since  the  difference  in  temperature  between  the  air  of  the  egg  chamber 
and  the  air  of  the  room  is  one  of  the  factors  affecting  the  rate  of  flow 
of  air  through  an  incubator,  the  intake  and  exhaust  ventilators  need 
be  opened  less  at  the  beginning  of  the  incubation  period  in  a  cool  room 
than  in  a  warm  room.  They  should  then  be  opened  a  little  more  every 
few  days,  as  the  embryos  develop,  until  there  is  enough  air  passing 
through  the  egg  chamber  when  the  hatch  is  completed  so  that  the 
chicks  do  not  pant  from  a  lack  of  fresh  air. 

The  incubator  manufacturer  whose  instructions  are  to  open  the 
ventilators  after  the  first  week  and  nearly  close  them  again  on  the 
nineteenth  day  is  tacitly  admitting  that  his  machine  is  either  over- 
ventilated  with  the  ventilators  wide  open  or  defective  in  moisture 
supply.     If  over-ventilated,  fuel  is  being  wasted  from  a  too  rapid 


1928]  ARTIFICIAL   INCUBATION   OF    EGGS  13 

circulation  of  air  through  the  egg  chamber  (a  very  important  matter 
with  an  electric  incubator  operating  on  a  house  lighting  rate).  If 
adequately  ventilated  with  the  ventilators  wide  open  on  the  eighteenth 
day,  they  should  not  be  closed  on  the  nineteenth  day.  The  ventila- 
tion requirements  of  the  chicks  at  this  time  are  increasing  and  not 
diminishing.  Restricting  ventilation  to  cause  the  humidity  of  the 
egg  chamber  to  increase  while  the  chicks  are  hatching  should  not  be 
necessary  if  the  moisture  device  in  the  incubator  is  functioning 
properly  in  regulating  the  humidity  of  the  egg  chamber. 

Moisture. — The  process  of  breathing  in  the  developing  egg  is 
closely  analogous  to  that  in  human  beings.  The  exhaled  air  is  laden 
with  moisture,  and  it  is  as  a  result  of  giving  off  moisture  in  this  way 
that  the  eggs  "dry  down"  during  embryonic  growth.  In  this  drying 
down  process  there  is  a  gradual  loss  of  the  w7ater  content  of  the  egg 
and,  as  previously  indicated,  a  correspondingly  gradual  increase  in  the 
size  of  the  air-cell.  When  the  air  passing  through  the  egg  chamber 
is  very  dry,  however,  it  not  only  takes  up  and  carries  off  the  moisture 
naturally  exhaled  by  the  egg,  but  may  pass  through  the  porous  shell 
and  absorb  still  more  moisture.  Such  excessive  drying  down  is 
detrimental.  It  is,  therefore,  necessary  to  have  the  air  passing  through 
the  egg  chamber  sufficiently  charged  with  moisture  to  prevent  any 
undue  evaporation  of  water  from  the  egg. 

Ventilation  and  moisture  conditions  are  closely  related  and  cannot 
be  considered  separate  problems.  Geographical  location,  time  of  year, 
and  other  factors  must  determine  whether  artificial  means  of  adding 
moisture  to  the  air  entering  the  egg  chamber  are  necessary  or  not. 
In  the  better  types  of  incubators,  ventilation  is  very  well  taken  care 
of,  so  that  the  chief  problem  to  consider  is  the  maintenance  of 
sufficient  moisture  in  the  circulating  air.  One  should  always  follow 
the  instructions  sent  out  by  the  incubator  manufacturer  in  this  regard 
until  sufficient  experience  has  been  gained  to  enable  one  to  act 
intelligently  in  making  any  change  that  may  appear  advisable. 

During  the  period  of  incubation  frequent  observation  of  the  air- 
cells  will  indicate  the  rate  of  evaporation  of  the  egg  and  will  help 
one  to  determine  if  too  much  or  too  little  moisture  is  being  supplied. 
Experience  will  soon  teach  one  the  normal  rate  of  evaporation  as 
shown  by  a  gradual  increase  in  the  size  of  the  air-cell.  It  is  a  good 
plan,  however,  for  the  beginner  to  set  a  hen  on  the  ground  in  an 
out-door,  bottomless  setting  coop  where  the  earth  is  reasonably  moist 
and  well  shaded  at  the  same  time  that  he  sets  the  incubator  and  to 
compare  the  increase  in  the  size  of  the  air-cell  in  both  cases  every 
few  days. 


14  CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE  [ClRC.  19 

Yet  another  method  of  checking  the  rate  of  evaporation  of  water 
from  the  eggs  is  to  weigh  them,  as  was  done  by  Atwood  (1917).  He 
weighed  each  tray  when  set  and  again  at  the  same  time  each  day 
during  the  period  of  incubation.  From  these  weighings  he  worked 
out  the  following  tabulation  indicating  the  normal  loss  in  weight  of 
one  hundred  eggs  day  by  day  for  the  first  nineteen  days, 

Day                                  Ounces  Day                                  Ounces  Day                                  Ounces 

1 1.65  8 13.44  15 25.66 

2 3.31  9 15.16  16 27.44 

3 4.96  10 16.88  17 29.21 

4 6  62  11 18.60  18 30.99 

5 8.28  12 20.33  19 32.77 

6 10.00  13 22.10 

7 11.72  14 23.88 

In  the  practical  use  of  Atwood 's  data,  weighing  the  eggs  when  set 
and  again  on  the  4th,  7th,  11th,  15th,  and  19th  days  should  be 
sufficient. 

After  the  chicks  have  begun  to  hatch,  optimum  humidity  of  the 
egg  chamber  is  indicated  by  a  light  film  of  moisture  or  a  few  beads 
of  water  appearing  along  the  lower  inside  edge  of  the  glass  of  the 
incubator  door,  whereas  a  considerable  accumulation  of  moisture  on 
the  glass  door  would  indicate  too  much  humidity.  This  latter  con- 
dition can  be  corrected  by  increasing  the  ventilation  or  by  reducing 
the  amount  of  moisture  supplied  to  the  air  of  the  egg  chamber. 

Tco  little  humidity  at  hatching  time  is  indicated  by  the  absence 
of  moisture  from  the  inside  of  the  glass  door,  and  by  the  rapid  drying 
and  whitening  of  the  shell  membranes  exposed  around  the  edges  of 
the  opening  where  the  chick  has  pipped  the  shell  and  before  it  has 
gotten  out.  As  the  shell  membranes  dry  they  become  tough  and 
difficult  for  the  chick  to  tear  through.  The  watery  albumen  coating 
the  inside  of  the  inner  shell  membrane  also  becomes  more  and  more 
viscid  with  loss  of  moisture,  and  serves  to  glue  the  membranes  to  the 
chick  and  retard  its  efforts  to  escape  from  the  shell.  The  membranes 
should  remain  moist  while  the  chick  is  breaking  out  of  the  shell,  for 
they  are  then  soft  and  easily  torn  and  do  not  adhere  to  the  chick's 
body. 

The  humidity  of  the  eg£-  chamber  can  be  increased  by  means  of 
wet  sponges  or  cloths,  by  sprinkling  the  eggs,  by  inserting  shallow 
pans,  etc.  The  sponges,  cloths,  and  pans  can  be  suspended  above  the 
eggs  or  placed  below  them.  Saturated  sand  can  be  placed  in  the 
pans  in  lieu  of  water  and  will  aid  in  hastening  evaporation  as  the 
moist  particles  of  sand  present  a  larger  evaporating  surface  than 
does  a  level  water  surface.     These,  however,  are  more  or  less  make- 


1928]  ARTIFICIAL    INCUBATION    OF   EGGS  15 

shift  methods  of  providing  moisture  and  cannot  be  compared  with  a 
well  designed,  built-in  system  of  humidity  control. 

Turning  the  Eggs. — Turning  is  usually  begun  forty-eight  hours 
after  the  eggs  are  put  into  the  incubator,  and  continued  daily  until 
the  first  egg  pips,  Hannas  (1920),  however,  obtained  best  results 
when  turning  was  begun  on  the  first  day.  Turning  should  be  done 
at  least  twice  and  preferably  three  or  four  times  a  day,  if  automatic 
turning  trays   are   used. 

The  results  obtained  to  date  at  the  California  Agricultural  Experi- 
ment Station  indicate  that  frequent  turning  of  the  eggs  each  day  is 
beneficial.  Payne  (1921)  also  observed  favorable  results  from  fre- 
quent daily  turning.  The  eggs  do  not  have  to  be  turned  completely 
over.  All  that  is  necessary  is  to  move  them  around  so  that  each  egg 
is  turned  more  or  less. 

Cooling. — Cooling  is  intended  to  air  the  eggs  and  it  is  said  to 
strengthen  the  embryos.  It  corresponds,  perhaps,  to  the  opening  of  all 
of  the  windows  by  the  housewife  each  morning  to  air  the  bedroom. 
Data  is  steadily  accumulating,  however,  to  indicate  that  cooling  is  of 
no  real  value  to  the  eggs  hatched  in  a  well  ventilated  incubator;  in  a 
deficiently  ventilated  incubator  it  is  undoubtedly  of  material  aid  to 
the  hatching  process  in  overcoming  inadequate  ventilation  of  the  egg 
chamber. 

When  eggs  are  cooled  the  trays  should  be  placed  on  the  top  of  the 
incubator  or  on  a  table.  No  part  of  the  tray  should  project  beyond 
the  table  or  incubator  top  or  the  eggs  will  cool  unevenly.  The 
incubator  door  should  not  be  left  open  for  the  aim  is  to  cool  the  eggs, 
not  the  incubator.  The  hen's  body  temperature  is  the  same  when  she 
returns  to  the  eggs  as  it  was  when  she  left  them. 

Cooling  is  usually  begun  on  the  seventh  day,  and  the  eggs  cooled 
once  a  day  thereafter  till  the  first  egg  pips.  The  proper  length  of 
time  to  cool,  each  day,  is  generally  determined  by  the  eye  test,  In 
this  test  the  small  ends  of  a  few  eggs  are  held  to  the  eye  and  when 
they  feel  barely  warm  it  is  considered  that  sufficient  cooling  has  been 
given.  During  the  early  part  of  the  incubating  period  the  eggs  will 
cool  down  more  or  less  rapidly,  depending  on  the  temperature  of  the 
room,  but  as  the  embryos  grow,  cooling  will  take  place  more  slowly, 
other  things  being  equal. 

Testing. — The  eggs  are  usually  tested  the  first  time  between  the 
fourth  and  eighth  day  of  incubation  and  again  between  the  fourteenth 
and  eighteenth  days.  The  purpose  of  the  first  test  is  to  remove  all 
infertile  eggs  and  the  dead-germ  eggs  up  to  that  time.     In  this  first 


16 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE 


[Circ.  19 


test  the  dead-germ  eggs  will  generally  appear  addled  or  show  blood 
clots  or  blood  rings.  Every  egg  in  which  a  dark,  movable  spot,  with 
numerous  radiating  blood  vessels,  is  not  distinctly  visible  at  this  time 
should  be  discarded.  Only  strong-germed  eggs  will  hatch  vigorous 
chicks. 

On  the  fourteenth  day  the  eggs  containing  living  embryos  will  be 
largely  opaque,  with  a  reddish  cast  to  the  lighter  areas  and  with  large 
blood  vessels.  Dead  germs  will  show  less  development  and  no  large 
blood  vessels,  and  the  lighter  areas  will  have  a  pale  yellow  appearance. 
These  dead-germ  eggs  as  well  as  the  infertile  eggs,  can  be  hard  boiled 
with   the   shells   on    (held    at    boiling    temperature    for   at   least    30 


Dead  germ,  seventh  day.  Fertile  egg,  seventh  day. 

Fig.  2     (From  Circular  233) 


Infertile  egg. 


minutes),  ground  fine  in  a  meat  grinder,  and  fed  to  growing  chicks, 
mixed  into  the  dry  mash  two  or  there  times  a  week  at  the  rate  of  one 
egg  to  twenty-five  or  more  chicks. 

The  Hatch. — After  the  first  egg  pips,  the  incubator  should  not  be 
opened  again  until  the  hatch  is  over.  When  the  hatch  is  completed, 
as  evidenced  by  the  presence  of  no  more  wet  chicks  on  the  egg  trays, 
the  trays  can  be  removed.  If  the  chicks  in  the  nursery  trays  pant,  the 
incubator  doors  should  be  wedged  open  enough  to  stop  the  panting 
without  cooling  the  egg  chamber  sufficiently  to  cause  a  thermometer 
on  the  egg  tray  to  fall  below  100°  F.  After  wedging  open  the  doors 
the  flame  (if  using  an  oil  or  gas  heated  incubator)  may  have  to  be 
turned  up  to  keep  the  chicks  comfortable.  The  egg  chamber  should 
be  kept  dark  to  keep  the  chicks  quiet.  This  can  be  done  by  fastening 
paper  or  dark  cloth  over  the  incubator  doors. 

Twenty-four  hours  after  the  hatch  is  completed  the  chicks  can  be 
removed  to  the  brooder.  Many  poultrymen  like  to  put  them  in  warmed 
day  old  chick  boxes  when  the  egg  trays  are  removed  instead  of  holding 
them  in  the  nursery  till  they  are  taken  to  the  brooder. 


1928  ]  ARTIFICIAL    INCUBATION    OF    EGGS  17 


TURKEY  AND   OTHER    EGGS 

The  available  evidence  to  date  would  indicate  that  turkey  and 
duck  eggs  and  the  eggs  of  other  domestic  fowl  should  receive  the  same 
treatment  as  hen  eggs  when  incubated  artificially.  These  eggs  would 
seem  to  have  the  same  requirements  as  regards  temperature,  ventila- 
tion, turning,  cooling,  and  moisture  as  the  eggs  of  the  hen. 


BIBLIOGRAPHY 

Atwood,  H. 

1917.  The  incubation  of  hen  eggs.  West  Virginia  Agr.  Exp.  Sta.  Circ.  25: 
1-24. 

Benjamin,  E.  W. 

1920.  A   study  of   selections   for   the   size,   shape,    and    color   of   hen's    egg. 

Cornell  Agr.  Exp.  Sta,  Memoir  31:195-312. 
Dareste,  C. 

1883.  Nouvelles  recherches  sur  la  production  des  monstres,  dan  1  'oeuf  de 
la  poule,  par  l'effet  de  1 'incubation  tardive.  Comp.  Rend.  96: 
444-446. 

Dougherty,  J.  E. 

1915.     Incubator  temperatures.     California  Agr.  Exp.  Sta.  Ann.  Ept.  1914- 

15:37-38. 
1926.     Studies  in  incubation.     The  effect   of  low  temperatures  previous   to 

incubation   on   hatchability    of   eggs   set.      Am.   Jour.   Physiol.   79: 

39-43. 

Dougherty,  J.E.,  and  S.  S.  Gossman. 

1923.  Observations  on  tint  in  white  eggs.  California  Agr.  Exp.  Sta.  Ann. 
Ept.  1922-23:221-222. 

Edwards,  C.  L. 

1902.     The   physiological   zero    and   the    index    of    the    egg    of    the    domestic 
fowl,  Gallus  domesticus.     Am.  Jour.  Physiol.  6:351-397. 
Elford,  F.  C. 

1921.  Dominion  of  Canada,  Dept.   Agr.,   Interim  Rpt.   Poultry   Husbandman 

for  year  ending  March,  1921:3-29. 

Gowell,  G.  M. 

1902.  Experiments  in  incubation.  Maine  Agr.  Exp.  Sta.  Eighteenth  Ann. 
Kept. :  18-25. 

II  ANN  AS,   E.   E. 

1020.  Embryo  mortality.  Jour.  Am.  Assn.  Inst.  Invest.  Poultry  Husbandry 
6:77-79. 

Lamson,  G.  H.,  and  H.  D.  Edmond. 

1914.     Carbon  dioxide  in  incubation.     Storrs  Agr.  Exp.  Sta.  Bui.  76:219-258. 


18  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [ClRC.  19 

Mauro,  F. 

1923.  II  trattamento  frigarifieo  della  nova   (di  gallina)    e  la  sur  influenza 

sulla  capacita  di  sviluppos  della  macula  germinativa.  Atti  della 
Soc.  Ital.  de  Seienz  62:239.  (Abstr.  in  Institute  Internat.  Du 
Froid.  Monthly  Bui.  Information  on  Refrigeration.  English  ed. 
5:5-508.) 

Mussehl,  E.  F.,  and  P.  Bancroft. 

1924.  Effect  of  low  temperatures  on  hatching  power  of  hen's  eggs.     Poultry 

Sci.  4:79. 
Payne,  L.  F. 

1921.     A    study   of   multiple    turning   of   incubated   eggs.     Jour.    Am.    Assn. 
Instruct.  Invest.  Poultry  Husbandry  7:17-20. 

Philips,  A.  G. 

1909.     Keeping  eggs  for  hatching.     Kansas  Farmer  47:3-7. 

Waite,  R,  H. 

1919.     The  effect  of  age  of  eggs  on  their  hatching  quality.     Maryland  Agr. 
Exp.  Sta.  Bui.  233:87-101. 


STATION   PUBLICATIONS   AVAILABLE   FOR  FREE   DISTRIBUTION 


BULLETINS 


No.  No. 

253.   Irrigation   and   Soil   Conditions  in   the  3  86. 

Sierra    Nevada   Foothills,    California. 

262.  Citrus   Diseases  of   Florida   and   Cuba  3  87. 

Compared   with   those   of    California.  388. 

263.  Size  Grades  for  Ripe  Olives. 

268.   Growing  and  Grafting  Olive  Seedlings  389. 

273.   Preliminary  Report  on   Kearney  Vine-  390. 

yard     Experimental     Drain,     Fresno 
County,    Calif.  391. 

277.  Sudan  Grass. 

278.  Grain   Sorghums.  392. 

279.  Irrigation  of  Rice  in  California.  393. 
283.  The  Olive  Insects  of  California.  394. 
304.   A   Study  of  the  Effects  of   Freezes  on 

Citrus  in  California. 

310.   Plum  Pollination.  395. 

313.   Pruning      Young      Deciduous      Fruit 

Trees.  396. 

324.   Storage  of  Perishable  Fruits  at  Freez- 
ing Temperatures.  397. 

328.    Prune    Growing  in    California. 

331.   Phylloxera-resistant   Stocks.  398. 

335.   Cocoanut   Meal    as   a    Feed   for   Dairy  400. 

Cows   and    Other   Livestock.  402. 

340.   Control     of     the     Pocket     Gopher     in  404. 

California.  405. 

343.  Cheese    Pests   and   Their   Control.  406. 

344.  Cold    Storage    as   an   Aid   to   the   Mar-  407. 

keting  of  Plums,  a  Progress  Report. 

347.  The  Control  of  Red  Spiders  in  Decid- 

uous Orchards.  408. 

348.  Pruning  Young  Olive  Trees.  409. 

349.  A     Study    of     Sidedraft    and    Tractor 

Hitches. 

350.  Agriculture     in      Cut-Over      Redwood 

Lands.  410. 

353.  Bovine    Infectious    Abortion,    and    As- 

sociated Diseases  of  Cattle  and  New- 
born  Calves.  411. 

354.  Results  of  Rice  Experiments  in   1922. 

357.  A    Self-Mixing    Dusting    Machine    for  412. 

Applying  Dry  Insecticides  and  Fun- 
gicides. 

358.  Black    Measles,     Water    Berries,     and  414. 

Related  Vine  Troubles. 

361.  Preliminary   Yield   Tables  for   Second-  415. 

Growth    Redwood.  416. 

362.  Dust  and   the   Tractor   Engine. 

363.  The   Pruning  of  Citrus  Trees  in  Cali-  417. 

fornia. 

364.  Fungicidal    Dusts    for   the    Control    of  418 

Bunt. 

366.  Turkish     Tobacco     Culture,     Curing,  419. 

and   Marketing. 

367.  Methods  of  Harvesting  and  Irrigation  420. 

in  Relation  to  Moldy  Walnuts. 

368.  Bacterial      Decomposition      of      Olives  421. 

During   Pickling.  422! 

369.  Comparison      of     Woods     for     Butter 

Boxes.  423. 

370.  Factors    Influencing    the    Development 

of  Internal  Browning  of  the  Yellow  424. 

Newton   Apple. 

371.  The    Relative    Cost   of   Yarding    Small  425. 

and   Large   Timber.  426 

373.  Pear   Pollination. 

374.  A    Survey    of    Orchard    Practices    in  427. 

the     Citrus     Industry     of     Southern 
California.  428. 

375.  Results   of    Rice    Experiments    at    Cor- 

tena,    1923,  and  Progress  in  Experi- 
ments in   Water  Grass  Control  at  the  429 
Biggs   Rice   Field    Station,    1922-23.  430' 

377.   The  Cold  Storage  of  Pears.  431 

3  79.   Walnut   Culture   in   California. 

380.   Growth    of    Eucalyptus    in    California  432. 

Plantations. 

382.   Pumping    for    Draininge    in    the    San  433. 

Joaquin   Valley,    California. 

385.   Pollination  of  the  Sweet  Cherry. 


Bearing      Deciduous     Fruit 


Cali 
with 


Quality     of 
it    is    Har- 

Soil    Fumi- 


Pruninj 
Trees. 

Fig    Smut. 

The  Principles  and  Practice  of  Sun- 
Drying  Fruit. 

Berseem  or  Egyptian  Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat 
with    Copper   Carbonate   Dust. 

Fruit  Juice  Concentrates. 

Crop   Sequences  at  Davis. 

I.  Cereal  Hay  Production  in 
fornia.  II.  Feeding  Trials 
Cereal  Hays. 

Bark  Diseases  of  Citrus  Trees  in  Cali- 
fornia. 

The  Mat  Bean,  Phaseolus  Aconitifo- 
lius. 

Manufacture  of  Roquefort  Type  Cheese 
from  Goat's  Milk. 

Orchard    Heating   in    California. 

The   Utilization  of   Surplus  Plums. 

The  Codling  Moth  in  Walnuts. 

The  Dehydration  of   Prunes. 

Citrus    Culture   in    Central    California. 

Stationary  Spray  Plants  in  California. 

Yield,  Stand,  and  Volume  Tables  for 
White  Fir  in  the  California  Pine 
Region. 

Alternaria  Rot  of  Lemons. 

The  Digestibility  of  Certain  Fruit  By- 
products as  Determined  for  Rumi- 
nants. Part  I.  Dried  Orange  Pulp 
and  Raisin  Pulp. 

Factors  Influencing  the 
Fresh  Asparagus  after 
vested. 

Paradichlorobenzene  as  a 
gant. 

A  Study  of  the  Relative  Value  of  Cer- 
tain Root  Crops  and  Salmon  Oil  as 
Sources   of   Vitamin    A   for    Poultry. 

Planting  and  Thinning  Distances  for 
Deciduous  Fruit  Trees. 

The  Tractor  on   California  Farms. 

Culture  of  the  Oriental  Persimmon  in 
California. 

Poultry  Feeding  :  Principles  and  Prac- 
tice. 

A  Study  of  Various  Rations  for  Fin- 
ishing Range  Calves    as  Baby  Beeves. 

Economic  Aspects  of  the  Cantaloupe 
Industry. 

Rice  and  Rice  By-Products  as  Feeds 
for  Fattening  Swine. 

Beef   Cattle  Feeding   Trials,    1921-24. 

Cost  of  Producing  Almonds  in  Cali- 
fornia :   a  Progress  Report. 

Apricots  (Series  on  California  Crops 
and   Prices). 

The  Relation  of  Rate  of  Maturity  to 
Egg  Production. 

Apple  Growing   in   California. 

Apple  Pollination  Studies  in  Cali- 
fornia. 

The  Value  of  Orange  Pulp  for  Milk 
Production. 

The     Relation     of     Maturity     of 
fornia      Plums      to      Shipping 
Dessert  Quality. 
Economic  Status  of  the  Grape  Industry. 

Range  Grasses  of  California. 

Raisin  By-Products  and  Bean  Screen- 
ings as  Feeds  for  Fattening  Lambs. 

Some  Economic  Problems  Involved  in 
the  Pooling  of  Fruit. 

Power  Requirements  of  Electrically 
Driven     Manufacturing     Equipment. 


Cali- 
and 


No. 
434. 

435. 


436. 
437. 
438. 
439. 


No. 

87. 
115. 
117. 

127. 
129. 
136. 

144. 

157. 
164. 
166. 
173. 

178. 
179. 

202. 

203. 
209. 
212. 
215. 
217. 

230. 

231. 
232. 

234. 

238. 
239. 

240. 

241. 

243. 

244. 
245. 

248. 

249. 
250. 

252. 
253. 
254, 

255. 


BULLETINS- 


Investigations  on  the  Use  of  Fruits  in 
Ice  Cream  and  Ices. 

The  Problem  of  Securing  Closer 
Relationship  Between  Agricultural 
Development  and  Irrigation  Con- 
struction. 

I.  The  Kadota  Fig.  II.  Kadota  Fig 
Products. 

Economic  Aspects  of  the  Dairy  In- 
dustry. 

Grafting  Affinities  with  Special  Refer- 
ence to  Plums. 

The  Digestibility  of  Certain  Fruit  By- 
products as  Determined  for  Rumi- 
nants. Part  II.  Dried  Pineapple 
Pulp,  Dried  Lemon  Pulp,  and  Dried 
Olive  Pulp. 


(Continued) 
No. 

440.  The    Feeding    Value    of    Raisins    and 

Dairy  By-Products  for  Growing  and 
Fattening  Swine. 

441.  The  Electric  Brooder. 

442.  Laboratory  Tests  of  Orchard  Heaters. 

443.  Standardization    and    Improvement    of 

California    Butter. 

444.  Series  on  California  Crops  and  Prices  : 

Beans. 

445.  Economic    Aspects    of    the    Apple    In- 

dustry. 


CIRCULARS 
No. 


Alfalfa. 

Grafting   Vinifera   Vineyards. 

The  selection  and  Cost  of  a  Small 
Pumping   Plant. 

House  Fumigation. 

The  control  of  Citrus  Insects. 

Melilotus  Indica  as  a  Green-Manure 
Crop  for  California. 

Oidium  or  Powdery  Mildew  of  the 
Vine. 

Control   of   Pear   Scab. 

Small    Fruit    Culture    in    California. 

The   County  Farm  Bureau. 

The  Construction  of  the  Wood-Hoop 
Silo. 

The   Packing  of   Apples  in   California. 

Factors  of  Importance  in  Producing 
Milk   of  Low  Bacterial   Count. 

County  Organization  for  Rural  Fire 
Control. 

Peat   as    a   Manure    Substitute. 

The  Function  of  the  Farm  Bureau. 

Salvaging   Rain-Damaged   Prunes. 

Feeding   Dairy   Cows  in    California. 

Methods  for  Marketing  Vegetables  in 
California. 

Testing  Milk,  Cream,  and  Skim  Milk 
for  Butterfat. 

The   Home  Vineyard. 

Harvesting  and  Handling  California 
Cherries   for   Eastern  '  Shipment. 

Winter  Injury  to  Young  Walnut 
Trees  During  1921-1922. 

The   Apricot   in    California. 

Harvesting  and  Handling  Apricots 
and  Plums  for  Eastern  Shipment. 

Harvesting  and  Handling  California 
Pears  for  Eastern   Shipment. 

Harvesting  and  Handling  California 
Peaches  for  Eastern   Shipment. 

Marmalade  Juice  and  Jelly  Juice 
from   Citrus  Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine   Pruning   Systems. 

Some  Common  Errors  in  Vine  Prun- 
ing and  Their  Remedies. 

Replacing  Missing  Vines. 

Measurement  of  Irrigation  Water  on 
the  Farm. 

Support   for   Vines. 

Vineyard   Plans. 

The  Use  of  Artificial  Light  to  In- 
crease Winter  Egg  Production. 

Leguminous  Plants  as  Organic  Fer- 
tilizers  in    California   Agriculture. 


257. 

258. 
259. 
261. 
264. 

265. 
266. 

267. 

269. 
270. 
273. 

276. 

277. 

278. 
279. 
281. 


282. 

283. 

284. 
286. 
287. 
288. 
289. 
290. 
292. 
293. 
294. 
296. 

298. 

300. 
301. 
302. 
304. 
305. 
306. 

307. 
308. 
309. 
310. 

311. 


The  Small-Seeded  Horse  Bean  (Vicia 
faba   var.   minor). 

Thinning    Deciduous   Fruits. 

Pear  By-Products. 

Sewing  Grain   Sacks. 

Preliminary  Essentials  to  Bovine  Tu- 
berculosis  Control   in    California. 

Plant   Disease  and   Pest   Control. 

Analyzing  the  Citrus  Orchard  by 
Means  of  Simple  Tree  Records. 

The  Tendency  of  Tractors  to  Rise  in 
Front;   Causes  and  Remedies. 

An   Orchard   Brush   Burner. 

A  Farm   Septic  Tank. 

Saving  the   Gophered   Citrus  Tree. 

Home    Canning. 

Head,  Cane  and  Cordon  Pruning  of 
Vines. 

Olive  Pickling  in  Mediterranean 
Countries. 

The  Preparation  and  Refining  of 
Olive  Oil  in   Southern  Europe. 

The  Results  of  a  Survey  to  Deter- 
mine the  Cost  of  Producing  Beef  in 
California. 

Prevention  of  Insect  Attack  on  Stored 
Grain. 

Fertilizing  Citrus  Trees  in   California. 

The   Almond   in   California. 

Milk  Houses  for  California  Dairies. 

Potato   Production   in    California. 

Phylloxera   Resistant  Vineyards. 

Oak   Fungus   in    Orchard    Trees. 

The  Tangier  Pea. 

Alkali   Soils. 

The    Basis    of    Grape    Standardization. 

Propagation    of   Deciduous   Fruits. 

Control  of  the  California  Ground 
Squirrel. 

Possibilities  and  Limitations  of  Coop- 
erative Marketing. 

Coccidiosis  of  Chickens. 

Buckeye  Poisoning  of  the  Honey  Bee. 

The    Sugar   Beet  in   California. 

Drainage  on  the  Farm. 

Liming  the   Soil. 

A  General  Purpose  Soil  Auger  and 
Its  Use  on   the  Farm. 

American   Foulbrood   and   Its   Control. 

Cantaloupe    Production    in    California. 

Fruit  Tree   and   Orchard   Judging. 

The  Operation  of  the  Bacteriological 
Laboratory  for  Dairy  Plants. 

The   Improvement  of   Quality  in   Figs. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


15m-5,'28 


